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Nancy J. Coletta, Anne Moskowitz, Hyunjeong Han; Pupil displacement in videokeratoscopy is correlated with axial length. Journal of Vision 2005;5(12):55. doi: 10.1167/5.12.55.
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© ARVO (1962-2015); The Authors (2016-present)
The pupil often appears to be displaced temporally from the center of corneal topography maps; this effect, known as videokeratoscope shift, is consistent with the typical deviation of the eye's optical and visual axes. Videokeratoscope shift decreases with increasing myopia (Bansal et al., 2004) but it is also determined by corneal power (Mandell, 1994). Myopia is associated with changes in corneal power as well as axial length, so we examined the relationship of videokeratoscope shift to these two refractive components. Axial length, corneal radius and pupil displacement were obtained from 18 adults whose refractions ranged from +2.25 D to −14.75 D. Axial length was highly correlated with refraction (r=0.91; p<0.0001) but corneal power also increased with myopia (r=0.45; p=0.058). Horizontal pupil displacement decreased significantly with increasing axial length (r=0.49; p=0.04) while it showed no trend with corneal radius of curvature (r=0.21; p=0.396). The correlation of pupil displacement with axial length implies that the relative position of the optical and visual axes depends on eye shape, which is known to vary with axial elongation. The optical axis could be tilted in myopia, or the fovea could be shifted in the nasal direction relative to the optical axis position at the retina.
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